1. Field of the Invention
The present invention generally relates to an apparatus for continuously manufacturing a molding compound such as, for example, TMC (thick molding compound) or SMC (sheet molding compound) by kneading a resinous paste together with reinforcement material such as, for example, glass fibers or Carbon fibers and sandwiching the kneaded mixture between a pair of carrier sheets. In particular, the present invention relates to a resin supply device employed in the molding compound manufacturing apparatus for continuously supplying a resinous paste material, with or without the reinforcement material mixed therein, uniformly in a direction widthwise of each carrier sheet used to sandwich the resinous paste material.
2. Description of the Prior Art
The prior art molding compound manufacturing apparatus of the type referred to above and to which the present invention is applicable is disclosed in, for example, U.S. Pat. No. 3,932,980, issued Jan. 20, 1976, to Mizutani et al. and assigned to the assignee of the present invention, and is reproduced in FIG. 9. Referring to FIG. 9, the molding compound manufacturing apparatus shown therein comprises a chopping unit for breaking a plurality of glass rovings A to form chopped reinforcement glass fibers, a paste supply unit including a batch tank 8 containing a quantity of a resinous paste material B, and a pair of carrier films C and C' each in the form of a sheet or the like.
The chopping unit includes a cutter roll 1 for chopping the glass rovings A into chopped glass fibers of a predetermined length which then fall by gravity into a hopper positioned beneath the chopping unit. Impregnating rolls 3 and 3' are positioned immediately below the hopper for mixing a curtain of the falling glass fibers with the resinous paste material which has been supplied dropwise from perforated supply tubes 2 and 2' onto the peripheral surfaces thereof, respectively. The resinous paste mixed with the glass fibers and adhering to the impregnating rolls 3 and 3' is removed from the impregnating rolls 3 and 3' by scraper rolls 4 and 4' positioned immediately beneath the respective impregnating rolls 3 and 3' and held in contact therewith. The resinous paste removed from the impregnating rolls 3 and 3' and containing the chopped glass fibers subsequently falls by gravity towards an adjoining region, at which the carrier films C and C' adjoin together, and is then sandwiched between the carrier films C and C' as the latter are drawn in one direction while resting on a belt conveyor 5. As the carrier films C and C' with the resinous paste sandwiched therebetween pass through a nipping region between shaping rolls 6 positioned on a downstream side of the adjoining region with respect to the direction of travel of an upper run of the belt conveyor 5, the thick molding compound is produced.
As shown in FIG. 9, each of the paste supply tubes 2 and 2' has an axial length substantially equal to that of the corresponding impregnating roll 3 or 3' and supported is immediately above and parallel to the associated impregnating roll 3 or 3' while spaced a predetermined distance therefrom. Each of these paste supply tubes 2 and 2' has one end 2b and 2b' closed and the opposite end 2a and 2a' fluid-coupled with a constant volume pump 9 through a main supply tube 7 by way of a generally T-shaped coupling, the constant volume pump 9 being in turn fluid-communicated with the batch tank 8 so that the resinous paste material B within the batch tank B can be supplied by the constant volume pump 9 to the paste supply tubes 2 and 2' through the main supply tube 7.
A ribbon-shaped portion of each paste supply tube 2 and 2' which confronts the associated impregnating roll 3 and 3' positioned immediately therebelow is perforated to provide a respective row of perforations 2c and 2c' spaced a predetermined distance from each other in a direction axially thereof. The resinous paste material supplied into the paste supply tubes 2 and 2' in the manner described above can thus be supplied dropwise onto the associated impregnating rolls 3 and 3' through the perforations 2c and 2c'.
The paste supply tubes 2 and 2' employed in the prior art molding compound manufacturing apparatus have been found to have the following problem. The molding compound manufacturing apparatus works satisfactorily for some time subsequent to the start of production of the thick molding compound with the resinous paste material smoothly and uniformly discharged through the perforations 2c and 2c' in the paste supply tubes 2 and 2'. However, since the paste supply tubes 2 and 2' are closed at their free ends 2b and 2b' remote from the main supply tube 7, and as the apparatus continues to be operated, the resinous paste material supplied into the paste supply tubes 2 and 2' and brought to a standstill in the vicinity of the closed ends 2b and 2b' of the respective paste supply tubes 2 and 2' forms puddles of resinous paste material. The puddles of resinous paste material at the closed ends of the paste supply tubes 2 and 2' increase in viscosity with passage of time to thereby form viscid leftovers. These viscid leftovers of resinous paste material once formed downstream of the respective paste supply tubes 2 and 2' with respect to the direction of flow of the resinous paste material expand in a direction upstream of the respective paste supply tubes 2 and 2' with the further passage of time unless removed by cleaning, thereby causing clogging of some of the perforations 2c and 2c' adjacent the closed ends 2b and 2b'.
Once this occurs, the cascade flow of resinous paste material discharged from respective rows of perforations in each paste supply tube 2 and 2' becomes narrower. That is, the discharge of the resinous paste material from the perforations 2c and 2c' in the respective paste supply tubes 2 and 2' becomes such that it is supplied onto the impregnating rolls 3 and 3' in a quantity smaller at the downstream side than that at the upstream side with respect to the direction of flow of the resinous paste material within the paste supply tubes 2 and 2'. Consequently, uniform distribution of the resinous paste material over the substantially entire length of each impregnating roll 3 and 3' is no longer obtained. Uneven distribution of the resinous paste material over the impregnating rolls 3 and 3' resulting from the presence of the biased viscid leftovers within the paste supply tubes 2 and 2' eventually results in a production of the tick molding compound having a thickness varying in a direction across the width W thereof.
The molding compound manufacturing apparatus may be utilized to form a multi-layered sheet of molding compound such as SMC and the foregoing problems can be equally found in this type of multi-layered sheet manufacturing apparatus.
As discussed hereinabove, failure of the paste supply tubes to dispense the resinous paste material uniformly over the substantially entire length of the impregnating rolls results in the formation of the thick molding compound having a thickness varying in a widthwise direction thereof. Therefore, it has been a routine practice to bring the apparatus to a halt and then to clean the paste supply tubes by the use of a suitable solvent such as, for example, ethyl acetate. This cleaning of the paste supply tubes is carried out generally at regular intervals of 2 to 3 hours subsequent to the start of production of the thick molding compound and, for this reason, the efficiency of production tends to be lowered.
The cascade flow of resinous paste material when reduced in width for the reason discussed above results in the production of the thick molding compound having a width, only part of which can be used as a material for a molded product.
Also, the thick molding compound having the thickness varying widthwise poses a problem when it is wound around a take-up reel or hub for storage. Specifically, as the thick molding compound is wound around the take-up reel to thereby form a roll of thick molding compound, the resultant roll of thick molding compound has an increased outer diameter at one end as compared with the outer diameter at the opposite end thereof and the winding of the thick molding compound will soon become unstable.